In recent years, it has become increasingly common to provide turbochargers on compression ignition, internal combustion engines. A turbocharger utilizes the hot exhaust gases of the engine as its power source, and it provides a substantial pressure boost in the air intake manifold. A turbocharged engine is thereby able to deliver greater horsepower than a comparable size engine without a turbocharger.
During the operation of such an engine, the ratio of the mass of the fuel to the mass of the air in the cylinders is an important factor. The fuel-to-air ratio affects the power output and the efficiency of the engine, and it has an effect on the amount of pollution produced by the engine. This ratio usually is generally constant over the normal operating speed range of the engine.
A problem encountered in turbocharged engines concerns the maintenance of the desired fuel-to-air ratio. For example, when the throttle is opened to accelerate the engine, the fuel charge is able to increase more rapidly than the air charge. The air charge does not increase as rapidly because the turbocharger cannot quickly respond to the demand for an increase in the supply of air. The result is an over-rich mixture of fuel and air, which is undesirable for a number of reasons.
Some turbocharged engines have been equipped with aneroids in an attempt to eliminate the above problem. Prior art aneroids have been designed to respond to the air intake manifold pressure and to prevent a rapid increase in the quantity of injected fuel during a period of acceleration, until the turbocharger is able to increase its speed and meet the demand for additional air. Such prior art aneroids have not been satisfactory because they have not maintained the desired proportion or ratio between fuel and air, the ratio has not been consistent and predictable, and they have required a start valve for deactivating the aneroid at low engine speeds.